1. Field of the Invention
The present invention relates to a method for controlling vehicle automatic transmission systems, and more particularly to a control method for an automatic transmission system which includes a friction type clutch and a gear type transmission and is electronically controlled in accordance with the operation condition of the associated vehicle to perform automatic gear-shift operations.
2. Description of the Prior Art
The conventional automatic transmission system of the type described above uses gear-shift map data for determining a suitable gear position for the operation condition of the vehicle at each moment, and the gear-shifting operation of the transmission is automatically performed in accordance with the determination. With this system, since the target gear position determined is liable to change frequently if the operating condition of the vehicle is not stable, unnecessary gear-shift operations will be carried out. This will give an uncomfortable feeling to the vehicle passenger.
To overcome this drawback, in the Japanese Patent Application Public Disclosure No. Sho 60-252852 there is proposed a gear-shifting control method for inhibiting unnecessary gear-shifting operations by making it possible to carry out a gear-shifting operation only after the change in the amount of the operation of the acceleration pedal has become steady.
However, according to the proposed method, in the case where an operation parameter or parameters other than the amount of operation of the accelerator pedal becomes unstable, for example in the case the level of the output signal of a vehicle speed sensor becomes unstable due to noise coming from outside or insufficient electrical contact of a connector, the target gear position will change rapidly and cause unnecessary gear-shifting operations to be carried out frequently.